1. Field of the Invention
The present invention relates to an ignition coil unit for use in a distributorless ignition system for an internal combustion engine and more particularly to an ignition coil unit arranged in the vicinity of the associated spark plugs of an engine.
2. Description of the Related Art
With a known distributorless ignition system of the type in which a high voltage is supplied to each spark plug from an ignition coil through a high tension cord, if, for example, the plurality of ignition coils are each arranged above one of the spark plugs by utilizing the unused space between the two camshafts of a double overhead cam (DOHC) type engine, a high tension cord is arranged within the extremely small space between the ignition coil and the spark plug with the resulting deterioration of the mounting property and mounting efficiency of the ignition coils.
Thus, an ignition system has been proposed in the past in which the ignition coil and the spark plug are connected with an integral supply plate to make the system more compact (e.g., Nippondenso Open Giho, Code No. 38-175, published on Nov. 15, 1984). This conventional ignition system is disadvantageous in that the supply plates are arranged at the bottom of the small unused space between the two camshafts and therefore the mounting or demounting of the supply plates during the assembling or inspection of the spark plugs is not easy.
Also, an ignition system has been proposed in which a single ignition coil is provided for each pair of spark plugs in such a manner that one of the high tension couplers of each ignition coil is directly connected to one spark plug and the other high tension coupler is connected to the other spark plug through a high tension cord (e.g., Nippondenso Open Giho, Code No. 30-032, published on Apr. 20, 1983). This conventional ignition system is disadvantageous in that since the other high tension coupler of the ignition coil is connected to the other spark plug through the high tension cord, it is difficult to mount and demount the high tension cords within the small space.